It has been common practice in the automotive industry to mount the various engine drive accessories, such as the generator/alternator, power steering pump, air conditioning compressor, engine water pump, exhaust air pump, etc. to the front of the engine with a variety of separate brackets. This practice allowed the position of the accessories to be varied in order to fit different applications. It also allowed the position of the accessories to be adjusted in order to tension the drive belt. Individually mounted accessories also allowed different accessory combinations or "packages" to be mounted on a particular engine, such as may be necessary depending upon the different options ordered with a given vehicle. With these accessory packages, many of the accessories were typically mounted to different surfaces of the engine. This resulted in many of the accessories lying in different planes and thus required the utilization of multiple belts.
It has also been known to mount the engine drive accessories in one or more parallel planes allowing them to be driven with a plurality of V belts from a crankshaft pulley. This configuration provided a reliable, quiet, efficient and economical power transmission system, but still suffered from various problems, including the fact that the accessories were mounted to engine surfaces that were positioned in different planes. Instead of multiple belts, a single serpentine multi-rib V belt has also been utilized to drive all the accessories that were positioned in a single plane by utilizing both sides of the belt.
Regardless of the number of belts used, controlling belt tension in order to reduce wear thereon is a significant design concern. Belt tension has typically been controlled with a spring loaded pulley for automatic continuous adjustment of tension as well as to take-up any slack from belt stretch or wear in the system. These arrangements compensate for belt wear and help to prolong belt life, which is a significant concern for automotive manufacturers who want to warrant belt life for 100,000 miles or more. However, other significant factors also contribute to belt wear, including mounting tolerances and pulley alignment.
Therefore, a large amount of development effort has gone into refining these belt drive systems to make them more durable, quiet, and efficient. However, many problems remain. Developing solutions to these problems has been made more challenging by the demands for drive belt systems having higher durability that also have quieter operating levels.
Two primary problems still exist with current vehicle belt drive systems. The first primary problem is the need for accurate alignment of the drive accessories, each having their own belt pulleys, to provide optimum belt operating conditions. The second primary problem is to provide rigid mounting of the drive accessories so that the system as a whole is free from noise, vibration, and harshness ("NVH") in the form of troublesome resonant vibrations.
Regarding the first problem, the alignment of the belt pulleys is influenced by a variety of factors, including the number of drive components incorporated in a given system, their dimensions and the number of surfaces to which the components are attached. Each of these components have separate tolerances. Thus, as the number of components and different surfaces to which the components are attached increases, the tolerances add up to higher than desired amounts. These added tolerances make it more difficult to align the drive accessories in one plane and also increases the manufacturing and assembly costs if one attempts to align the drive accessories in one plane through tighter tolerances.
Additionally, traditional mounting brackets have been made with materials and processes such as stampings and castings that also have large tolerances. Machining the mating surfaces can help reduce the tolerances, but this still does not reduce the number of separate interfaces. Further, the surfaces on the engine used for mounting the brackets, such as the cylinder head and the engine block, also have tolerances relative to each other which add to the total variation in pulley alignment, which also affects the NVH quality of the system.
Regarding the second problem, the mounting bracket systems that attach the accessories to the engine also require a certain stiffness to prevent resonant vibration response of the accessories to forcing frequencies from the engine or the accessories. Typically, modern engine systems can easily have forcing frequencies in the range of 350-390 Hz. It has been difficult to design bracket systems that have response frequencies of this level or above. Many factors contribute to this design difficulty, including accessory spacing requirements to obtain acceptable belt run lengths; multi-piece brackets to accommodate different accessory combinations; space requirements to accommodate hoses, wires and their connections; long stand-off distances to accommodate long components such as the water pump; weight and cost limitations on the bracket structure; mounting methods of the accessories themselves; and the need for tools and serviceability of individual accessories.